1. Field of the Invention
The present invention relates to computing. More particularly, the present invention relates to the creation of the secure delivery of multicast content over a network.
2. Description of the Related Art
Internet Protocol (IP) broadcasting involves the transmission of content to multiple clients on a network via the IP protocol. IP broadcasting is part of the broader field of multicasting, which involves any transmission of content to multiple destinations simultaneously. As such, multicasting includes not only IP broadcasting but also more traditional broadcasts such as cable or satellite television broadcasts, and includes content that can be delivered via channels, or schedules of programming usually delineated by genre or distributor.
In IP broadcasting, channel content is delivered over an IP network via multicasting. The user selects the channel he wants to view and a terminal IP broadcasting device, such as a set-top box, starts receiving and displaying the content in real time.
Multicasting can be distinguished from other types of content delivery services such as Video-on-demand (VOD) streaming and content downloading. In VOD streaming, the user chooses a particular piece of content from a list of available contents and the service provider starts streaming the content whenever the user wishes. Thus, upon the request of the user, a terminal device (e.g., set-top box) asks the service provider to start streaming the content, receives it, and displays it.
In the content download model, a user is able to download content to a storage medium (e.g., a hard drive of a set-top box) and view it anytime afterwards.
Thus, while IP broadcasting is a multicast model, VOD and content download are unicast models.
Key concepts in IP Multicast include an IP multicast group address, a multicast distribution tree, and receiver driven tree creation. An IP Multicast group address is used by sources and receivers to send and receive content. Sources use the group address as the IP destination address in outgoing data packets, while receivers use the group address to inform the network that they are interested in receiving packets sent to the group. The protocol used by receivers to join a group is the Internet Group Management Protocol (IGMP).
Once receivers join a particular IP Multicast group, a multicast distribution tree is constructed for that group. The protocol most widely used for this is Protocol Independent Multicast (PIM). It sets up multicast distribution trees such that data packets from sends to a multicast group reach all receivers that have joined the group.
IP Multicast does not require a source sending a given group to know about any of the receivers in the group. The multicast tree construction can be initiated by network nodes that are close to, or at the receivers. This allows it to scale to a large receiver population.